The present invention relates to a device for impregnation of webs composed of porous materials.
More particularly, it relates to an impregnating device which has a roller rotatable about a horizontal axis, a trough for dipping in at least partially with a chamber provided between the trough and the roller, and an impregnating medium supply insert in the chamber.
Devices of the above mentioned general type are known in the art. One of such devices is disclosed for example in the patent document EP 0 173 519 B1. In this device the impregnation is performed with a liquid impregnating medium under increased pressure. Thereby substantially greater quantities of the impregnating medium can be introduced into substrate than in the case of pressureless impregnation. It is for example possible to impregnate dense paper with low suction properties. Furthermore, there is also a possibility to use impregnating media with high viscosity, or in other words with high solid matter content and low solvent matter content. The required pressure increase is obtained in particular so that the chamber which receives the impregnating medium continuously narrows from an inlet slot in direction toward an outlet slot. The throughgoing web drives the border layer of the impregnating medium adhering to its outer surface into the narrowing region of the chamber. Thereby the pressure in the chamber increases in direction toward the outlet slot. With through go speeds of substantially 45-60 m/s, and the conditions disclosed in the reference a pressure in the vicinity of the outlet slot which is the value which is substantially over 1 MPa. When the impregnating medium is supplied by a pressure pump, the static pressure produced by the pressure pump adds to the dynamic pressure produced in the chamber.